perf: modify the default free quota of Niutrans

feat: add support for Tencent Translate

feat: add support for Bing Dictionary

perf(UI): adjust blue text button expandValue and vertical padding

feat: add support for Caiyun translate

feat: add support for Niutrans

fix: app starup crashes when user perferred language is only one(tisf…

…eng#225)

fix: app crash when front most app is nil

fix: app crash when startup

feat: add support for Apple Dictionary